Drive for a hold down assembly of a can bodymaker a method of use thereof

ABSTRACT

A drive for use in the manufacture of cans comprises a hydraulically powered guide pod to which a hold down assembly is attached. The guide pod slides along a guide rod which is fixed in the bodymaker. Forward and rear hydraulic chambers are defined between the pod and the guide rod by means of bushings and a seal. Passage of fluid through ports to and from the hydraulic chambers causes the pod and hold down assembly to move forward and backward. The length of the stroke can be set by the distance between the ports. A rotary valve is used to control the timing of the drive and control flow of hydraulic fluid, which is typically obtained from the bodymaker coolant supply.

BACKGROUND OF THE INVENTION

This invention relates to a drive for a hold down assembly for use inthe manufacture of cans. In particular, but not exclusively, it relatesto a drive for a blank holder which holds a can blank against a redrawdie.

Hold down mechanisms such as redraw sleeves and blanking punches areknown. Typically, a lever is held against cam profiles on the crank. Thelever drives a pair of push rods to drive a crosshead which, in turn,actuates a blank holder. This combination of push rods and cam actuationmoves the blank holder towards a redraw die to bring the can blank, orcup, to the die. The blank holder presses the base of the cup against aflat face of the die while a punch pushes the cup into the die forredrawing.

This type of mechanism is heavy and the rotating mass on the crankshaftpresents a severe load to the bodymaker main bearings. This inventionseeks to reduce problems associated with this loading.

SUMMARY OF THE INVENTION

According to the present invention there is provided a hydraulic drivefor a hold down apparatus in a can bodymaker, the drive comprising afixed guide rod; a guide pod surrounding the guide rod, the pod havingrear and forward end faces which together define rear and forwardhydraulic chambers respectively, the chambers being separated by a seal;a first channel (A) for the passage of hydraulic fluid to and from therear hydraulic chamber via a return stroke port; a second channel (B)for the passage of hydraulic fluid to and from the forward hydraulicchamber via a forward stroke port; whereby passage of fluid into theforward chamber drives the pod and hold down assembly connected theretoto a forward position and passage of fluid into the rear chamber forcesthe pod and hold down assembly to return to a back position.

By using a hydraulically powered drive, the rotating mass on thebodymaker crankshaft is dramatically reduced since the existing pushrods, cam levers, redraw cams and cam followers and air bags to hold thecam followers onto the cams are no longer required. This in turndecreases the size of the bodymaker hydraulic power pack which isrequired for the push rods, cams and followers in known hold downapparatus. Furthermore, an increase in machine speed is possible due tothe reduction in mass and subsequent reduction in system inertia whichcould lead to increased production.

Various knock-on effects are achieved by the use of the hydraulic drivefor the hold down assembly, such as a reduction in size of powercomponents, flywheel and other drives etc. and thereby reducing load onthe bodymaker main bearings and wear.

The rear and forward end faces of the pod may typically be defined bybushings.

The hydraulic fluid may be the machine coolant which is typicallyalready available in the factory supply. Although this may require ofthe order of 60 liters/minute, the bodymaker hydraulic power pack can infact be reduced in size due to the replacement of several components asnoted above. The replacement operation is possible simply by means of aretro-fit.

The forward chamber typically comprises a substantially cylindricalportion which tapers radially outwardly at its forward end wherebypressure in the hydraulic chamber is decreased at the forward end. Thetaper, or chamfer decreases hydraulic pressure at the forward end of thehydraulic chamber since the chamber size is increased at the fluidpressure face but limits fluid requirements in the remainder of thechamber.

The hydraulic drive may ideally include check valves for controllinginitial acceleration of the guide pod and/or pressure relief valves forthe avoidance of pressure spikes.

Whilst the hydraulic fluid flow may be controlled by a variety of means,ideally a rotary valve is used. The rotary valve may rotate at a speedwhich is less than or equal to machine speed, according to the desiredmachine timing.

According to a further aspect of the present invention, there isprovided a method of driving a hold down apparatus in a bodymaker, themethod comprising: providing a fixed guide rod; connecting the hold downapparatus to a guide pod which surrounds the guide rod and is movablealong the guide rod, the pod having rear and forward end faces whichdefine rear and forward hydraulic chambers respectively, the chambersbeing separated by a seal; supplying hydraulic fluid to and from therear hydraulic chamber via a return stroke port; supplying hydraulicfluid to and from the forward hydraulic chamber via a forward strokeport; whereby supplying fluid into the forward chamber drives the podand hold down assembly connected thereto to a forward position andsupplying fluid into the rear chamber forces the pod and hold downassembly to return to a back position.

Preferably, the end faces comprise bushings for covering and/or openingthe ports, and the method further comprises: accelerating movement ofthe pod and hold down apparatus by uncovering a port and increasingfluid flow to and from the respective chamber; or decelerating themachine stroke by covering a port and reducing fluid flow to and fromthe respective chamber.

Preferred embodiments of hydraulic drive will now be described, by wayof example only, with reference to the drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial side section of a bodymaker showing hydraulic driveand hold down;

FIG. 2 is an enlarged side section of the drive of FIG. 1;

FIG. 3 is an enlarged partial side section of an alternative drive;

FIG. 4 is an alternative hold down assembly; and

FIG. 5 is a side section of the rotary valve of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a side section of a bodymaker front end with a hydraulicdrive 1 for actuation of hold down assembly 10. A rotary valve 20controls flow of hydraulic fluid as will be described in more detailbelow.

As shown in FIGS. 2 and 3, drive 1 consists of a central guide rod 2 andguide pod 3, to which the hold down assembly 10 is connected. The pod 3has an inner portion 12 which may typically be made of steel so that theguide rod 2 bears against this inner sleeve 12. In order to limit massand inertia, the pod outer portion 13 is of lighter material, typicallyaluminium.

Annular space between inner sleeve 12, guide rod 2 and forward and rearbushings 14, 15 is separated into forward and rear chambers 6, 9respectively by labrynth seal 11. Guide rod 2 is fixed in position inthe bodymaker so that supply of hydraulic fluid to and from forward andrear chambers 6 and 9 forces the pod 3 to move forwards and backwardsalong the guide rod 2 according to the pressure of hydraulic fluid inthe chambers 6 and 9.

Conduits A and B provide channels for passage of hydraulic fluid betweenrotary valve 20 and the guide rod 2. As shown in FIG. 2, channel A leadsvia port 7 and/or rear cushion jets 8 to rear chamber 9. Similarly,channel B leads via port 4 and/or forward cushion jets 5 to forwardchamber 6. The operation of the ports and cushion jets is described inmore detail below. In the embodiment of FIG. 3, check valves 5′, 8′ areprovided in the forward and rear chambers 6, 9 respectively and pressurerelief valves 46 are provided in the chamber 43. The operation of thesevalves is also described in more detail below.

Forward chamber 6 comprises a cylindrical portion 16 which tapersoutwardly at its forward end 17 to fluid pressure face 18. The outwardtaper is defined by the degree of chamfer at the forward end of sleeve12. Although no equivalent change in size is provided for the returnstroke chamber 9, clearly this is possible within the scope of theinvention.

Referring now to FIGS. 1 and 4, hold down assembly 10 comprises a blankholder 30 for holding a cup 31 against redraw die 32. In the embodimentshown in FIG. 1, the hold down apparatus includes a spacer 33 andcentring ring 34. This centring ring 34 provides for ready access tochange the blank holder without the need for lengthy realignmentprocedures. A retainer 35 and spring 36 may be used instead of thespacer 33, as shown in FIG. 3.

FIG. 4 is a side section of a rotary valve 20 which is used to regulateflow of hydraulic fluid in a preferred embodiment of the invention. Ascan be seen in FIG. 1, valve 20 supplies fluid to drives 1 on both sidesof the hold down apparatus 10. Conduits A and B are in each drive unitare connected to drillings A and B in the rotary valve.

Valve 20 is connected to rotor shaft 21 which is driven by the bodymakermain crankshaft and rotates in the direction indicated by the arrow inFIG. 4. Hydraulic fluid from the bodymaker coolant supply enters therotary valve via inlet 22 and exits via exhaust 23. Inlet 22 and exhaust23 are shown out of position in FIG. 4 for clarity. A central bore 24 inthe shaft 21 connects inlet 22 and exhaust 23 to drillings A or B in thevalve according to the desired machine timing. The valve 20 is mountedon a manifold 40 which is bolted onto the bed of the machine.

Operation of the hydraulic drive of the invention is as follows.Pressurised hydraulic fluid from the bodymaker coolant supply issupplied to the bore 24 of central rotor shaft 21 by the action of anaccumulator and pump (not shown). As the central shaft 21 rotates,hydraulic fluid passes from the shaft 21 into drilling A when the rotaryvalve is in the position shown in FIG. 4. Drilling A suppliespressurised fluid along channel A to chamber 9 to drive the return stokeof the hold down.

In the embodiment shown in FIG. 4, the drillings A and B are offset inorder to achieve the desired machine timing. For example, the rotaryvalve may rotate at half machine speed (set by the crankshaft) in orderto limit component wear.

Drilling B in rotary valve 20 communicates with the exhaust 23 toexhaust medium in channel B when drilling A is aligned with channel A asshown. Similarly, drilling A communicates with the exhaust 23 to exhaustmedium in channel A.

The return stroke of the hold down apparatus occurs when the drilling Aof the valve is aligned with channel A as shown in FIG. 4. The returnstroke returns the hold down apparatus to the back position.

With reference to FIGS. 1 and 2, passage of fluid from channel A tochamber 9 is blocked by rear bushing 15 but can exit radially outwardsinto the rear chamber 6 through cushion jets 8. This ensures arelatively gentle start to movement of the pod 3 and hold down assemblyaway from the cup 31 in redraw die 32 as pressure builds up in rearchamber 9.

As the pressure increases further in the rear chamber, the movement ofthe pod 3 causes rear bushing 15 gradually to expose return stroke port7 and allows fluid to pass through the increasingly exposed port 7,thereby providing further acceleration of the return stroke until theport is fully open.

According to the drive timing (set by the valve 20), rotation of theshaft 24 in the valve assembly causes drilling A gradually to close.Meanwhile, movement of the forward bushing 14 causes hydraulic fluid inthe forward chamber 6 to exhaust out via channel B. As port 4 is closedby the bushing 14, movement of the pod is slowed until the trailing edgeof the port is closed. This deceleration is controlled further by theprovision of forward cushion jets 5 which restrict further exhaust andenhance the cushioning effect at the end of the return stroke. Thestroke length is determined by the position of the ports 4 and 7 in theguide rod.

As drilling B in the valve assembly opens, pressurised fluid passes frominlet 22 via central bore 24 to conduit B. The forward stroke to drivethe hold down assembly forward is then initiated as fluid graduallyenters the forward chamber 6 via cushion jets 5. Acceleration of theforward stroke occurs as forward bushing 14 uncovers forward stroke port4. Meanwhile, fluid from rear chamber 9 is exhausted through channel Ato exhaust 23 in the rotary valve. Slowing of the forward stroke isachieved in like manner to that of the return stroke as forward bushingcovers the port 4 and fluid enters the forward chamber through a reducedarea of port 4 and finally only via cushion jets 8. The cup 31 is thenheld against the die 32 for redrawing by movement of punch 45 into thecup.

It can be seen from FIG. 2 in particular that the forward and rearbushings 14, 15 provide for acceleration and deceleration of the pod 3at each end of the forward and return strokes as the bushings graduallyclose and/or uncover forward and rear ports 4, 7 respectively.

In the embodiment of FIG. 3, check valves 5′, 8′ are provided which areclosed on the exhaust stroke but open for the pressure stroke, therebyallowing fluid to chamber 6 or 9 respectively. This dead ends the fluidwhich is used to stop the guide pod 3 and applies pressure to the faceof associated bushing 14 or 15 until the supply groove is uncovered.

Pressure relief valves 46 prevent the build up of pressure due to fluidcompression in chamber 6 or 9 from reaching the point at which pressurespikes occur. Pressure is thus released via channel 41 and pressurerelief valves 46.

The hold down apparatus remains in the forward position as the punch 45enters cup 31 for redrawing. The cycle then repeats.

Any coolant which is forced between the guide rod 2 and the sleeve 16can be removed by the labrynth seal 11. Swarf or other debris collectsin annuli 42 in the bushings 14 and 15 and exits through passages 41into chamber 43 in the pod 3 to be passed out via port 44 for processingby the coolant supply.

The invention has been described above by way of example only andchanges may be made within the scope of the invention as defined by theclaims. For example, in the first embodiment shown in FIG. 2, movementof the pod is controlled not only by the bushings moving over the portsbut also by the use of cushion jets 5 and/or 8 between the channels andrespective hydraulic chambers. These cushion jets are positioned suchthat even after the bushing closes the ports, communication is stillpossible via the cushion jet or jets. In the second embodiment of FIG.3, a system of check valves is used to prevent “dead ending” of fluidwhich is used to stop the mechanism, and pressure relief valves for theavoidance of pressure spikes. Clearly any combination of cushion jetsand check and pressure relief valves may be used. Alternative featuresin either of the guide rod or guide pod (or both) which provide anenhanced soft start/stop to the movement of the guide pod are alsoconsidered to be within the scope of the invention.

Although a preferred embodiment of the invention has been specificallyillustrated and described herein, it is to be understood that minorvariations may be made in the apparatus without departing from thespirit and scope of the invention, as defined by the appended claims.

What is claimed is:
 1. A hydraulic drive for a hold down apparatus in acan bodymaker, the drive comprising a fixed guide rod; a guide podsurrounding the guide rod, the pod having rear and forward end faceswhich together define rear and forward hydraulic chambers respectively,the chambers being separated by a seal; a first channel (A) for thepassage of hydraulic fluid to and from the rear hydraulic chamber via areturn stroke port; a second channel (B) for the passage of hydraulicfluid to and from the forward hydraulic chamber via a forward strokeport; whereby passage of fluid into the forward chamber drives the podand hold down assembly connected thereto to a forward position andpassage of fluid into the rear chamber forces the pod and hold downassembly to return to a back position.
 2. The drive as defined in claim1 in which the rear and forward end faces are defined by rear andforward bushings.
 3. The drive as defined in claim 2 in which theforward chamber comprises a substantially cylindrical portion whichtapers outwardly at its forward end whereby pressure in the hydraulicchamber is decreased at the forward end.
 4. The drive as defined inclaim 1 in which the forward chamber comprises a substantiallycylindrical portion which tapers outwardly at its forward end wherebypressure in the hydraulic chamber is decreased at the forward end. 5.The drive as defined in claim 1 which further comprises a rotary valvefor controlling flow of hydraulic fluid.
 6. The drive as defined inclaim 5 in which the rotary valve rotates at a speed which is less thanor equal to machine speed.
 7. The drive as defined in claim 1 in whichthe stroke length of the pod and hold down apparatus is set by thedistance between the ports.
 8. The drive as defined in claim 1 in whichthe hydraulic fluid is obtained from the bodymaker coolant supply. 9.The drive as defined in claim 1 which further comprises a centering ringadjacent the blank holder.
 10. The drive as defined in claim 1 whichfurther comprises cushion jets and/or check valves for controllingacceleration of the pod.
 11. The drive as defined in claim 1 whichfurther comprises pressure relief valves.
 12. A method of driving a holddown apparatus in a bodymaker, the method comprising: providing a fixedguide rod; connecting the hold down apparatus to a guide pod whichsurrounds the guide rod and is movable along the guide rod, the podhaving rear and forward end faces which define rear and forwardhydraulic chambers respectively, the chambers being separated by a seal;supplying hydraulic fluid to and from the rear hydraulic chamber via areturn stroke port; supplying hydraulic fluid to and from the forwardhydraulic chamber via a forward stroke port; whereby supplying fluidinto the forward chamber drives the pod and hold down assembly connectedthereto to a forward position and supplying fluid into the rear chamberforces the pod and hold down assembly to return to a back position. 13.The method as defined in claim 12 in which the end faces comprisebushings for at least one of covering and opening the ports, the methodfurther comprising accelerating movement of the pod and hold downapparatus by uncovering a port and increasing fluid flow to and from therespective chamber; or decelerating the machine stroke by covering aport and reducing fluid flow to and from the respective chamber.
 14. Themethod as defined in claim 13 which further comprises reducing oreliminating occurrence of pressure spikes by providing pressure reliefvalves.
 15. The method as defined in claim 13 which further comprisescontrolling acceleration of the pod by opening check valves and allowingfluid to pass to the bushing until the port is uncovered.
 16. The methodas defined in claim 15 which further comprises reducing or eliminatingoccurrence of pressure spikes by providing pressure relief valves. 17.The method as defined in claim 12 which further comprises reducing oreliminating occurrence of pressure spikes by providing pressure reliefvalves.